The present invention relates generally to a process for treating wastes containing alkali metals, sulfur, heavy metals, boron compounds, and halogens. More specifically, the invention relates to a process for converting alkali metals, sulfur, heavy metals, and halogens into stable mineral forms through the use of a fluidized bed.
There exist many hazardous waste materials that are difficult to dispose because of the possibility that they may contaminate the environment. Such hazardous materials include compounds like heavy metals, sulfur, and halogens. These materials can be commonly found in many wastes, products, and compounds.
Typically, such hazardous waste is either buried or burned, both of which can be costly processes. Accordingly, it is desirable to process such wastes into materials that are more easily disposed of at lower costs. A large number of methods for treatment of such materials are known.
Alkali metals, which refer primarily to the elements of sodium and potassium, sulfur, and halogens are commonly found in such waste feed materials as sodium nitrate, potassium nitrate, sodium sulfates, and sodium chloride. In the past, such waste materials have typically been treated through processes like pyrolysis, incineration, and catalytic cracking. The catalytic cracking methods suffer from the draw back that they can only be used for treating materials having low contents of halogen-containing polymer materials. Further the cracking method is very expensive, and large acid resistant plants are needed for carrying out the method. Incineration processes are also disadvantageous, because these processes are becoming unacceptable from an environmental standpoint. Incinerators and related processes that utilize open-flame combustion fall under stringent and comprehensive air pollution laws that typically render the incinerators economically infeasible.
Pyrolysis methods are generally more flexible and can be used for the treatment of most waste materials. However, secondary waste streams that are generated from these processes, such as particulate waste and off gases, still present disposal issues that must be addressed.
Another problem associated with prior art waste processing methods involves sulfur-containing compounds. For example, the presence of such sulfur compounds in a vitrification melter can cause a molten sulfur salt pool to accumulate on top of the molten inorganic residue (glass). This pool causes high corrosion rates for the melter equipment. The pool can also have a high electrical conductivity, which causes short-circuiting of the heating electrodes in the melter. Additionally, potentially explosive conditions can result if large quantities of water contact the molten sulfur salt pool.
Further, the presence of heavy metals in the inorganic residues that may be present in the waste feeds can render the final waste product hazardous, thereby requiring additional processing of the residue before disposal or higher disposal costs. Also, the inorganic residue can contain soluble components that may form aqueous solutions after processing; these solutions can result in contamination of the surroundings after disposal.
Accordingly, there remains a need for a process that does not have the limitations and shortcomings of the above described methods for processing waste materials containing alkali metals, heavy metals, halogens, and sulfur.